1. Field of the Invention
The present invention relates to a structure mounted with an electronic component (hereinafter, also referred to simply as a mounted structure), which preferably has a rectangular or substantially rectangular parallelepiped shaped electronic component mounted on a wiring substrate via a solder joint material.
2. Description of the Related Art
In recent years, with requested downsizing of electronic devices, electronic components typified by resistive elements, capacitor elements, and the like as passive components have been progressively reduced in size. For example, laminated ceramic capacitors as a type of capacitor element has been exponentially reduced in size, and laminated ceramic capacitors with outside dimensions in the height direction, width direction, and depth direction all below 1.0 mm have been used widely.
In general, electronic components which have a pair of external electrodes provided on the surface of a body as a component main body, are mounted onto wiring substrates by joining with the use of a solder joint material so that the pair of external electrodes corresponds to a pair of lands provided for the wiring substrates.
Typically, the pair of external electrodes described above is often provided not only on the bottom surface of the body, which is opposed to the wiring substrate, but also even over a pair of end surfaces of the body, which is opposite in a predetermined direction, and moreover, often provided over not only the bottom surface and the pair of end surfaces, but also a pair of side surfaces and a ceiling surface, which are adjacent to the end surfaces (that is, so as to cover a pair of ends of the body located in the predetermined direction).
This configuration will, in the case of joining with the use of a solder joint material, cause the solder joint material to bank with wettability along the surfaces of the external electrodes provided to cover the end surfaces of the body, or the pair of side surfaces in addition to the end surfaces, a great self-alignment effect will be thus produced to mount the electronic component in a more appropriate position, and the joint strength between the electronic component and the wiring substrate will be kept high.
However, in the case of the electronic component configured as described above, it is known that a phenomenon of the electronic component mounted in a standing posture different from the intended posture on the wiring substrate is caused by the separation of one of the pair of external electrode from the wiring substrate in mounting the component. The phenomenon is typically referred to as a tombstone phenomenon or a Manhattan phenomenon, which is one type of defective mounting.
The phenomenon is caused by the generation of an imbalance between external forces applied to the electronic component due to the surface tension of the melted solder joint material banked with wettability on each end surface of the pair of external electrodes, and caused by various factors such as misalignment of the electronic component with respect to the wiring substrate during mounting, the shifted location of the solder joint material supplied, the excessive supply of the solder joint material, and asymmetric outlines of the pair of external electrodes.
Conventionally, from the perspective of preventing the phenomenon from being caused, measures such as increased positioning accuracy between respective components during mounting and the appropriately managed supply of the solder joint material are taken while making an attempt to increase the outline dimension accuracy for each component.
On the other hand, as another approach for preventing the phenomenon from being caused, JP 5-243074 A proposes that a metallic layer on which a solder joint material is unlikely to spread with wettability is formed so as to cover each end surface of a pair of external electrode.
However, the phenomenon has a tendency to be caused at increased frequency as the electronic component to be mounted is reduced in size, and has become obvious as an especially large problem in extremely compact electronic components with outside dimensions of 0.5 mm or less in the height direction, the width direction, and the depth direction.
More precisely, even when the supply of the solder joint material is appropriately managed while an attempt is made to increase the outside dimension accuracy for each component, it is extremely difficult in the first place to handle extremely compact electronic components with a high degree of accuracy, there is thus a natural limit to the increased positioning accuracy between the respective components during mounting, and the frequency of the phenomenon is not able to be sufficiently reduced just by this measure.
Moreover, when the approach disclosed in JP 5-243074 A as mentioned above is adopted, firstly, a problem occurs which is that the self-alignment effect described above is significantly damaged to make misalignment likely to be caused in relation to the mounting position of the electronic component, and secondly, in the case of extremely small electronic components as described above, it is difficult in the first place to form a metallic layer on which the solder joint material is unlikely to spread with wettability, so as to cover each end surface of the pair of external electrodes.